The present invention relates to improvements to electrolytic cells, especially to cells for the production of chlorine from aqueous solutions of alkali-metal chlorides.
This invention relates more particularly to a bipolar electrode for a diaphragm type electrolyser, said electrode comprising a substantially vertical supporting wall, a plurality of substantially vertical, spaced parallel anode plates, transversely connected to said wall, on one side thereof, and a plurality of substantially vertical, spaced, foraminate cathode fingers, transversally connected to the opposite side of said wall, and alternating with the anodes.
In known bipolar electrodes of this type, for example in the one described in the Belgian Pat. No. 752,380 of June 23, 1970 in the name of PPG INDUSTRIES Inc., the supporting plate is constituted by a steel plate to which the anodes (constituted by titanium plates coated with a catalytic active coating) and the cathodes (hollow cathode fingers having foraminate walls intended to be covered with a diaphragm) are fixed by welding, rivetting or bolting. On the anodic side, the steel plate is coated with a protective layer corrosion resistant to the electrolyte and to the products generated by electrolysis.
The aforesaid known bipolar electrodes present many disadvantages. Their construction is not easy in particular due to the cumbersome supporting plate of generally important sizes. The assembling of anodes and cathodes on said plate is also complicated by the need to have a plate strictly plane and to realize a regular and precise distribution of anodes and cathodes along said plate.
Another important disadvantage of these known bipolar electrodes is the difficulty to handle said electrodes, in particular to diassemble the same, in order, for example, to replace a damaged anode or cathode.
In order to facilitate the assembling of the anodes on the supporting plate and to reduce the electrical resistance of the resulting assembly, the supporting plate is sometimes made of a composite plate constituted by a steel strip and a titanium strip closely joined to each other for example by explosion welding. Then, the titanium anode plates may be easily fixed on the titanium strip. However, it has been noted on practice, that composite titanium-steel plates rapidly deteriorate due to the formation of titanium hydride in the titanium-strip, resulting from the diffusion of hydrogen atoms arising on the cathode surface.